One of the fundamental tenets of sensory biology is that sensory systems adapt to environmental change. It has been argued that adaptation should have the effect of optimizing sensitivity to the new environment. To make this premise concrete and precise, the proposed research builds on a normative theory of visual motion perception, which argues that the visual system will adapt optimally by balancing stimulus and measurement uncertainties. This theory makes predictions about visual spatiotemporal sensitivity as a function of environmental statistics: Adaptive optimization should be manifested as a change in spatiotemporal sensitivity for an observer and for the underlying motion-sensitive neurons. The proposed research will test these predictions. The effects of adaptation on visual sensitivity will be examined in the context of the neuronal representation of speed of visual motion. Adaptation using specific speeds will be used as a means to effect a change in environmental statistics. Both perceptual and neuronal consequences of this adaptation will be recorded, with the expectation that sensitivity changes will reflect the modeled process of optimization. The proposed research constitutes a richly interwoven collection of psychophysical, neurophysiological and theoretical approaches to the topic of visual adaptation. Experiments have been designed to yield an unprecedented body of comprehensive data bearing on the spatiotemporal properties of the primate visual system and the effects of environmental change. These data will be used to further understanding of the phenomenology and mechanism of adaptation.